Journal Talk 24: Mohammad & Oyon (2026)

The Local Group Mass from Hubble Flow Perturbations: A Bayesian Analysis of Modern Catalogs

Abstract

The total mass of the Local Group (LG) is a simple, but poorly determined parameter that controls the motions of its galaxies amongst themselves. In this paper we restudy this measurement, using the Hubble flow perturbation analysis of Peñarrubia et al. (2014), extended to include a quadrupole correction to the gravitational potential in a Bayesian formulation. We apply this methodology to 35 galaxies within 3 Mpc drawn from four catalogs of galaxies; the Local Group Volume Database, CosmicFlows-4, NED and HyperLeda. We measure the total mass of the LG, , and a mass ratio of Milky Way (MW) to Andromeda (M31), , with a statistical uncertainty almost 40% smaller than that obtained in previous studies. A significant contribution to the mass is likely to come from the intergalactic and circumgalactic medium. We have found that for the present-day accuracy of the mass distribution measurements, the quadrupole correction does not significantly influence the results, providing stronger constraints on the total mass, and a clearer picture of its distribution in the two dominant mass components of the Local Group.

Speakers:

• Sarker Mahathir Mohammad (Undergraduate Research Intern at CASSA; 3rd Year Undergraduate Student, Department of Physics, University of Dhaka)
• Hritom Sarker Oyon (Undergraduate Research Intern at CASSA; 1st Year Undergraduate Student, School of Physical and Mathematical Sciences, NTU Singapore)

Supervisor: Istiak H. Akib (Graduate Member of CASSA; LIRA, Observatoire de Paris, Université PSL, CNRS)